8 BULLETIN 1324, U. S. DEPARTMENT OF AGRICULTURE 
ing insects is not the morphological character of the host insect but 
of the gall which it inhabits. In some other parasites mentioned 
by this “author, the stimulus seems ‘to be furnished by the silken 
cocoons or webs of the host insects. 
ODOROUS SUBSTANCES 
A number of observations are on record which stress to a greater 
or less degree the importance of odor as a factor in oviposition. 
Scudder ( 71 ), in discussing the so-called botanical instinct of butter- 
flies, excludes taste and sight but believes the oviposition behavior is 
in keeping with the idea that the larval food plant is detected by 
means of the olfactory sense. Tragardh (79) places great emphasis 
_on chemotropism, and Picard (59) also emphasizes its importance 
but recognizes that light, temperature, humidity, and other physical 
factors play a part. Brues (77) states that there is much in the 
behavior of certain species to suggest that food plants are selected by 
the female insect on the basis of odor. In addition, Brues recog- 
nizes “some attribute of the plant, perhaps an odor, but far less pro- 
nounced to our senses than odor or taste” as a factor in the attraction 
of insects to plants. Grevillius (30) thought it probable that the 
choice of a food plant on the part of the brown-tail moth (/Luproctis 
chrysorrhoea) was determined by the olfactory sense. The cotton 
worm moth (Alabama argillacea Hbn.), which lays its eggs on the 
leaves of the cotton plant (Gossypium sp.), may be attracted by the 
nectar glands on the leaves (72). In fact, moths were seen alter- 
nately feeding from these glands and ovipositing. It was found, 
however, that no preference was shown for the portion near 
the glands on the involucre. This fact induced Comstock to 
question whether oviposition was here determined by the pres- 
ence of the nectar glands. Studies by McColloch (59) on Heli- 
othis obsoleta show that it deposits 60 per cent of its eggs on the 
silks when the corn plant is in silk. Artificial silks made of cotton 
twine soaked in the fresh juice pressed from corn silk received 79 
per cent of the eggs laid, while the controls (untreated cotton twine) 
received 21 per cent. Thus odor appears to be important in this 
case, but surfaces, according to MeColloch, must also be considered. 
Knoll (46) emphasizes the effect of odor upon Macroglossum stella- 
tarum when the moth is close to the plant upon which the eggs are to 
be laid. But green or yellow light is necessary to attract ‘the moth 
to the plant from a distance. The potato tuber moth is attracted by 
the odor of certain plants (67), but, as previously mentioned, the 
character of the surface is also highly important. Dewitz (20) 
thought the vine moth (Cochylis ambiguella) might be attracted and 
induced to lay its eggs upon or near the buds of the grapevine by the 
odor poured from the nectaries. But, in addition, he recognized the 
possible effect of contact stimulation. Loeb (49, p. 160) states that 
the blowfly © is attracted to and will oviposit on He ng meat but 
not on fat. It will also deposit eggs on objects smeared over with 
asafetida. A positive chemotr opism is responsible, according to this 
author, for oviposition. Tabre’s observations on the blow- fly, Calla 
5Jt is here called ‘“‘ the common house fly,’ but the reference is undoubtedly to one 
of the Calliphoras (cf. Loeb, 48). 
